1. Field of the Invention
The present invention relates generally to a device for indicating whether a fuse is operative or if it has blown.
Fuses are used in electrical systems to absorb any overload of current from the power source to the load. When the fuses are blown, the system served by the fuse is inoperative until the fuse is replaced. Often, however, it is difficult to determine whether a particular fuse is blown. Accordingly, a means for detecting when fuses are blown is necessary.
2. General Background
Fuse testers of various forms have been developed in the past, but those past testers have shortcomings regarding costs, ease of operation, and ability to test various sized fuses.
For example, U.S. Pat. No. 4,281,322 to Nasu et al. discloses a device for detecting blown fuses. Each of a plurality of fuses is arranged in series between a power source and a respective load. Light emitting diodes are connected between each of the fuses and its corresponding load. The diodes can be grounded by closing a switch, which cuts off the flow of current to the load and diverts the current through the diodes. In operation, closing the switch causes the light emitting diode connected to a particular fuse to light if the fuse is intact. If the fuse is blown, the corresponding diode will not light.
The Nasu et al. fuse testing device is incorporated with the electrical system and loads and does not test fuses independently of the system. This system uses a separate diode for each fuse, and there is no means for testing the light emitting diodes to insure that they are functioning properly.
U.S. Pat. No. 3,047,695 to Borys discloses a fuse testing system which is incorporated into a screw type cartridge fuse holder. The fuse tester is designed as a cartridge that houses both a single fuse and a testing apparatus. In the cartridge, a lamp and resistor are arranged in parallel relation to a fuse between a power source an a load. The fuse has a lower resistance than the resistor associated with the lamp. Thus, if the fuse is operable, current will flow from the power source to the load through the lower resistance fuse. If the fuse is blown, however, current will then flow through the lamp and resistor arrangement. Thus, a lit lamp indicates that the fuse is blown and an unlit lamp indicates that the fuse is intact.
Numerous other devices and systems have been designed for holding fuses and indicating when a fuse has been blown. Examples include those disclosed in U.S. Pat. Nos. 2,162,197 to Dodge; 2,206,787 to Linton; 2,225,912 to LaMar; 2,742,545 to Sundt; 2,758,295 to Sundt; 2,855,483 to Swing et al.; 4,025,888 to Judd et al.; 4,149,215 to Strich; and 4,443,780 to Huai-Chieh. While these devices and systems may be useful in indicating whether a particular fuse in a particular electrical application is in operation, the devices do not provide a simple and inexpensive device which can test fuses of various types and sizes, particularly fuses used in home and automobile systems which do not include sophisticated testing devices.